1. Field of the Invention
The invention relates to antenna systems and more particularly to scanning antenna systems with the capability of effecting desired gain versus scan characteristics over a prescribed spatial sector.
2. Description of the Prior Art
Prior art antenna systems which provide limited scan low sidelobe characteristics with a minimum number of active elements generally employ focal point systems such as lens or reflector type antennas with feed elements movably positioned in the focal region. This movement has been accomplished physically by traversing a feed element about the focal region to positions corresponding to the desired beams in space, or by placing a multiplicity of feed elements at predetermined locations in the focal region and selectively exciting the feed element or combination of elements through a complex switching network to establish the desired beams in space. Applications exist that require an antenna to scan tailor the scanned beam, that is, to provide narrow, high gain beams in one sector of the spatial volume and broad, lower-gain beams in another sector. Antennas of the prior art provided scan tailoring through selective defocussing by varying the phase and amplitude distribution from that required for a focussed beam or by positioning the feed elements predetermined distances forward of the focal plane.
Prior art feed networks capable of switchably coupling the electromagnetic energy to the feed elements and of exciting these elements to provide the required amplitude and phase distributions are characterized by considerable complexity, relatively high loss, and relatively high cost. It is the purpose of the present invention to provide a relatively simple, inexpensive system for switchably coupling electromagnetic energy to the elements of a focal plane scanning antenna to accomplish a desired limited scan function.